A youth wrestler in Illinois was socked in the face while trying to shake hands with his opponent following a match earlier this month ... and the blow was so violent, police are now investigating.
The altercation went down at the "Beat The Streets" tournament on April 8 at Oak Park River Forest H.S. in Oak Park, Ill., where kids from ages 8-to-18 were participating in a wrestling competition.
In video of the incident shot by The Wrestling Spot at the event, you can see an 8th grader from SPAR Academy and his opponent finishing up on the mat during a 125-128 pound freestyle third-place match -- when things suddenly took a disturbing turn.
The video shows as the SPAR wrestler -- who won the match 14-2 -- looked to shake hands with his opponent ... he was leveled by a cheap shot to the face.
The strike connected flush, and the SPAR wrestler -- wearing an orange and tan singlet -- crumpled to the floor.
TMZ Sports has learned he suffered a nose injury and has since been forced to wear a face mask at events while it heals ... but, fortunately, we're told he's somehow doing OK.
"He is making the best of the situation and is already back to training," SPAR Academy founder Justin Pearch told us Tuesday.
"As you may know, wrestling matches can get heated but nothing leading up to the punch would give cause to such bad decision-making on the opponent's part."
"It’s not tolerated in our sport and Spar Wrestling will never condone that behavior," Pearch added.
As for cops, an Oak Park Police Dept. spokesperson said Tuesday the incident is under investigation ... and the parents of both minors are cooperating.